U.S. patent application number 16/954916 was filed with the patent office on 2022-05-05 for method of producing copper alloy sheet material with excellent strength and conductivity and copper alloy sheet material produced therefrom.
This patent application is currently assigned to POONGSAN CORPORATION. The applicant listed for this patent is POONGSAN CORPORATION. Invention is credited to Jeongmin CHA, Youngchul CHOI, Jiin HWANG, Jangho JU.
Application Number | 20220136089 16/954916 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220136089 |
Kind Code |
A1 |
HWANG; Jiin ; et
al. |
May 5, 2022 |
METHOD OF PRODUCING COPPER ALLOY SHEET MATERIAL WITH EXCELLENT
STRENGTH AND CONDUCTIVITY AND COPPER ALLOY SHEET MATERIAL PRODUCED
THEREFROM
Abstract
Disclosed is a method of producing a copper alloy sheet
material, wherein the copper alloy sheet material contains nickel
(Ni) 0.5 to 1.5% by weight; cobalt (Co) 0.3 to 1.5% by weight;
silicon (Si) 0.35 to 0.8% by weight; chromium (Cr) 0.05 to 0.5% by
weight; a balance amount of copper (Cu); and inevitable impurities.
Further, disclosed is a copper alloy sheet material produced using
the method.
Inventors: |
HWANG; Jiin; (Ulsan, KR)
; CHOI; Youngchul; (Ulsan, KR) ; CHA;
Jeongmin; (Ulsan, KR) ; JU; Jangho; (Ulsan,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POONGSAN CORPORATION |
Pyeongtaek-Si |
|
KR |
|
|
Assignee: |
POONGSAN CORPORATION
Pyeongtaek-Si
KR
|
Appl. No.: |
16/954916 |
Filed: |
February 25, 2020 |
PCT Filed: |
February 25, 2020 |
PCT NO: |
PCT/KR2020/002654 |
371 Date: |
June 17, 2020 |
International
Class: |
C22F 1/08 20060101
C22F001/08; C22C 9/06 20060101 C22C009/06; B21B 1/26 20060101
B21B001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 2019 |
KR |
10-2019-0090805 |
Claims
1. A method of producing a copper alloy sheet material, wherein the
copper alloy sheet material contains the following component
elements: nickel (Ni) 0.5 to 1.5% by weight; cobalt (Co) 0.3 to
1.5% by weight; silicon (Si) 0.35 to 0.8% by weight; chromium (Cr)
0.05 to 0.5% by weight; a balance amount of copper (Cu); and
inevitable impurities, wherein the method comprises: melting and
casting the above component elements to form an ingot; hot-rolling
the ingot at 950 to 1040.degree. C.; cooling the hot-rolled
product; cold-rolling the cooled product at a cold reduction rate
of 70% or higher to form a copper alloy sheet material; performing
solid solution heat treatment of the sheet material at 800 to
1040.degree. C. for 20 to 60 seconds; and performing
thermal-mechanical double aging of the solid solution heat treated
sheet material, wherein the thermal-mechanical double aging
includes: performing first precipitation of the solid solution heat
treated sheet material at 550 to 700.degree. C. for 20 to 60
seconds; cold-rolling the first precipitated sheet material at a
cold reduction rate of 10 to 50%; and performing second
precipitation of the cold rolled sheet material at 300 to
550.degree. C. for 1 to 24 hours.
2. The method of claim 1, wherein a sum of contents of nickel (Ni)
and cobalt (Co) meets a following relationship:
1.5.ltoreq.Ni+Co.ltoreq.2.6, and wherein a ratio between contents
of nickel (Ni) and cobalt (Co) satisfies a following relationship:
0.8.ltoreq.Ni/Co.ltoreq.1.3.
3. The method of claim 1, wherein contents of nickel (Ni), cobalt
(Co), silicon (Si) and chromium (Cr) satisfies a following
relationship: 3.5.ltoreq.(Ni+Co)/(Si-Cr/3).ltoreq.4.5.
4. The method of claim 1, wherein the copper alloy sheet material
further contains at least one selected from a group consisting of
manganese (Mn) 0.01 to 0.2% by weight, phosphorus (P) 0.01 to 0.2%
by weight, magnesium (Mg) 0.01 to 0.2% by weight, tin (Sn) 0.01 to
0.2% by weight, zinc (Zn) 0.01 to 0.5% by weight, and zirconium
(Zr) 0.01 to 0.1% by weight.
5. A copper alloy sheet material produced using the method of one
of claims 1 to 4, wherein the copper alloy sheet material has a
microstructure containing an .alpha. mother phase and intermetallic
compound precipitates, wherein the intermetallic compound
precipitates has an average diameter of 3 .mu.m or smaller.
6. The copper alloy sheet material of claim 5, wherein 0.2% proof
stress of the copper alloy sheet material measured in a direction
parallel to a rolling direction thereof is in a range of 720 MPa to
820 MPa, wherein conductivity of the copper alloy sheet material is
in a range of 55% IACS to 60% IACS, wherein a 90.degree. bending
formability in a direction parallel to a rolling direction and a
direction perpendicular to a rolling direction of the copper alloy
sheet material is R/t=0.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method of producing a
copper alloy sheet material having excellent strength, conductivity
and bending formability, and a copper alloy sheet material produced
therefrom.
BACKGROUND ART
[0002] Recently, components (electronic components) constituting
electronic devices have been gradually downsized and refined.
Accordingly, characteristics required for a sheet material used for
the components are diversified. Characteristics required for a
connector among the electronic components are strength,
conductivity, bending formability, etc. Copper is mainly used as a
material that satisfies these characteristics. However, pure copper
has low strength. Thus, various types of copper alloys containing
one or greater elements to increase the strength are advantageously
used.
[0003] Hardening methods commonly used to increase strength of
alloys including the copper alloy include solid solution hardening,
work hardening, and precipitation hardening, etc. The solid
solution hardening allows an alloy element to be formed solid
solution in a matrix to lower purity of a matrix to rapidly
decrease conductivity. The work hardening tends to increase density
of dislocations in the matrix to decrease the conductivity. The
precipitation hardening may increase the purity of the matrix via
the nucleation and growth mechanism of precipitates and at the same
time effectively contribute to hardening. As a typical
precipitation hardened copper alloy, a copper (Cu)-nickel
(Ni)-silicon (Si)-based (so-called, Corson-based) alloy has
excellent bending formability and thus is often used for a
component with high workability such as a connector.
[0004] However, in recent years, as the electronic component has
been further miniaturized, thinning of the copper alloy sheet
material has been demanded. In order to overcome increase in
electrical resistance and decrease in load carrying capacity due to
the thinning, it is necessary to improve strength and conductivity.
Further, in order to improve the strength, an amount of nickel (Ni)
should be increased. However, when the nickel addition amount
exceeds 2.6% by weight, it is difficult to avoid formation of
coarse particles having a precipitate size exceeding 3 .mu.m. Since
the coarse particles act as a crack initiator during bending and
deteriorate the bending formability, it is difficult to achieve
both of the required properties of the strength and the bending
formability at the same time in the existing Colson-based
alloy.
[0005] Conventionally, in order to solve this problem, a method is
proposed in which cobalt (Co) or chromium (Cr) is added alone or in
combination to the Colson-based alloy, and then, solid solution
heat treatment is executed, and, then, one or two times additional
heat treatments are carried out, and then a last cold rolling is
performed, thereby improving strength and conductivity of the
alloy.
[0006] Specifically, Japanese Patent No. 6385383 intends to improve
properties by adding nickel (Ni), silicon (Si), cobalt (Co), and
chromium (Cr) in a copper alloy sheet material. However, this
approach may not simultaneously achieve conductivity of 55.0% IACS
or higher, and strength of 720 MPa or higher as 0.2% proof
stress.
[0007] Further, Japanese Patent No. 5647703 discloses that a total
content of nickel (Ni) and cobalt (Co) exceeded 3.0% by mass, and
the 0.2% proof stress exhibits excellent strength of 980 MPa or
greater. However, formation of coarse particles having a size
exceeding 3 .mu.m is not completely suppressed, and thus the
bending formability is deteriorated. Further, there is a limit that
conductivity of an obtained copper alloy sheet material could not
reach 45% IACS.
[0008] Further, in the above documents, a process mechanism for
facilitating cobalt (Co) precipitation during the production
process has not been clearly identified. Further, after performing
long-term or multiple precipitation heat treatments, finish rolling
is performed. Thus, solid solubility of the alloy element in the
copper matrix is rapidly reduced, and thus there is a limit in
achieving both of high strength and excellent conductivity at the
same time in the finish rolling.
DISCLOSURE
Technical Problem
[0009] A purpose of the present disclosure is to provide a method
of producing a copper (Cu)-nickel (Ni)-cobalt (Co)-silicon
(Si)-chromium (Cr) alloy sheet material having excellent strength
and conductivity using thermal-mechanical two-stages precipitation,
and to provide a copper alloy sheet material produced
therefrom.
Technical Solutions
[0010] According to the present disclosure, there is proposed a
method of producing a copper alloy sheet material, wherein the
copper alloy sheet material contains: nickel (Ni) 0.5 to 1.5% by
weight; cobalt (Co) 0.3 to 1.5% by weight; silicon (Si) 0.35 to
0.8% by weight; chromium (Cr) 0.05 to 0.5% by weight; a balance
amount of copper (Cu); and inevitable impurities, wherein the
method comprises: melting and casting the component elements (Ni,
Co, Si, Cr, and Cu) to form an ingot; hot-rolling the ingot at 950
to 1040.degree. C.; cooling the hot-rolled product; cold-rolling
the cooled product at a cold reduction rate of 70% or higher to
form a copper alloy sheet material; performing solid solution heat
treatment of the sheet material at 800 to 1040.degree. C. for 20 to
60 seconds; and performing thermal-mechanical double aging of the
solid solution heat treated sheet material, wherein the
thermal-mechanical double aging includes: performing first
precipitation of the solid solution heat treated sheet material at
550 to 700.degree. C. for 20 to 60 seconds; cold-rolling the first
precipitated sheet material at a cold reduction rate of 10 to 50%;
and performing second precipitation of the cold rolled sheet
material at 300 to 550.degree. C. for 1 to 24 hours.
[0011] A sum of contents of nickel (Ni) and cobalt (Co) meets a
following relationship: 1.5.ltoreq.Ni+Co.ltoreq.2.6, and a ratio
between contents of nickel (Ni) and cobalt (Co) satisfies a
following relationship: 0.8.ltoreq.Ni/Co.ltoreq.1.3.
[0012] Contents of nickel (Ni), cobalt (Co), silicon (Si) and
chromium (Cr) satisfies a following relationship:
3.5.ltoreq.(Ni+Co)/(Si-Cr/3).ltoreq.4.5.
[0013] The copper alloy sheet material further contains at least
one selected from a group consisting of manganese (Mn) 0.01 to 0.2%
by weight, phosphorus (P) 0.01 to 0.2% by weight, magnesium (Mg)
0.01 to 0.2% by weight, tin (Sn) 0.01 to 0.2% by weight, zinc (Zn)
0.01 to 0.5% by weight, and zirconium (Zr) 0.01 to 0.1% by
weight.
[0014] According to the present disclosure, there is proposed a
copper alloy sheet material produced using the method defined
above, wherein the copper alloy sheet material has a microstructure
containing an .alpha. mother phase and intermetallic compound
precipitates, wherein the intermetallic compound precipitates has
an average diameter of 3 .mu.m or smaller.
[0015] 0.2% proof stress of the copper alloy sheet material
measured in a direction parallel to a rolling direction thereof is
in a range of 720 MPa to 820 MPa, wherein conductivity of the
copper alloy sheet material is in a range of 55% IACS to 60% IACS,
wherein a 90.degree. bending formability in a direction parallel to
a rolling direction and a direction perpendicular to a rolling
direction of the copper alloy sheet material is R/t=0.
Advantageous Effects
[0016] The production method of the copper alloy sheet material
proposed from the present disclosure may produce the copper alloy
sheet material having excellent strength and conductivity and
excellent bending formability.
DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a process flow chart briefly showing a method of
producing a copper alloy sheet material with excellent strength and
conductivity according to the present disclosure.
[0018] FIG. 2 is a graph showing a phase fraction based on
temperature in a production process of a copper alloy sheet
material with the composition of Example 1.
[0019] FIG. 3 is a graph showing a molar fraction of each element
of Ni--Co--Si precipitates based on change in temperature that may
be applied to first and second precipitation heat treatments in a
production process of a copper alloy sheet material with a
composition of Example 1.
[0020] FIG. 4 is a graph showing a molar fraction of each element
of Ni--Co--Si precipitates based on change in temperature that may
be applied to first and second precipitation heat treatments in a
production process of a copper alloy sheet material having a
composition of Comparative Example 8.
BEST MODE
[0021] According to the present disclosure, there is proposed a
method of producing a copper alloy sheet material, wherein the
copper alloy sheet material contains the following component
elements: nickel (Ni) 0.5 to 1.5% by weight; cobalt (Co) 0.3 to
1.5% by weight; silicon (Si) 0.35 to 0.8% by weight; chromium (Cr)
0.05 to 0.5% by weight; a balance amount of copper (Cu); and
inevitable impurities, wherein the method comprises: melting and
casting the component elements (Ni, Co, Si, Cr, and Cu) to form an
ingot; hot-rolling the ingot at 950 to 1040.degree. C.; cooling the
hot-rolled product; cold-rolling the cooled product at a cold
reduction rate of 70% or higher to form a copper alloy sheet
material; performing solid solution heat treatment of the sheet
material at 800 to 1040.degree. C. for 20 to 60 seconds; and
performing thermal-mechanical double aging of the solid solution
heat treated sheet material, wherein the thermal-mechanical double
aging includes: performing first precipitation of the solid
solution heat treated sheet material at 550 to 700.degree. C. for
20 to 60 seconds; cold-rolling the first precipitated sheet
material at a cold reduction rate of 10 to 50%; and performing
second precipitation of the cold rolled sheet material at 300 to
550.degree. C. for 1 to 24 hours.
[0022] First, a composition range of the component elements of the
copper alloy sheet material according to the present disclosure
will be described in detail. In the description of the composition
range of the component elements in the present disclosure, %
representing a content of each component element means % by weight
unless otherwise indicated.
[0023] (1) Nickel (Ni)
[0024] A content of nickel (Ni) in accordance with the present
disclosure is in a range of 0.5 to 1.5% by weight. Nickel (Ni) is a
solid solution hardened element and is a precipitation hardened
element that forms an intermetallic compound with silicon (Si).
When the nickel (Ni) content is smaller than 0.5%, it is difficult
to secure strength. When the content exceeds 1.5%, it is difficult
to increase conductivity.
[0025] (2) Cobalt (Co)
[0026] A content of cobalt (Co) is in a range of 0.3 to 1.5%.
Cobalt (Co) forms a larger amount of fine intermetallic compounds
compared to silicon (Si) and nickel (Ni), and has an excellent
precipitation hardening effect. When the cobalt (Co) content is
smaller than 0.3%, it is difficult to secure the strength of the
obtained copper alloy. When the cobalt (Co) content exceeds 1.5%, a
solution heat treatment temperature range is reduced, so that there
is a possibility of forming a coarse intermetallic compound and
significantly reducing the precipitation hardening effect.
[0027] (3) Silicon (Si)
[0028] A content of silicon (Si) is range of 0.35 to 0.8%. Silicon
(Si) has a very large work hardening effect in the solid solution
state. Further, silicon (Si) forms an intermetallic compound with
nickel (Ni) and cobalt (Co), thus contributing to precipitation
hardening. When the silicon (Si) content is smaller than 0.35%, a
fraction of the intermetallic compound may be reduced, and thus an
precipitation hardening effect may be insignificant. When the
silicon (Si) content exceeds 0.8%, it is difficult to secure
conductivity and Si forms an oxide film on a surface, thereby to
reduce punchability.
[0029] (4) Chromium (Cr)
[0030] A content of chromium (Cr) is in range of 0.05 to 0.5%.
Since chromium (Cr) may allow silicon and the intermetallic
compound to be precipitated in a range below 980.degree. C., fine
intermetallic compounds may be formed in a grain boundary during
hot rolling, thereby minimizing a grain size. This may prevent
grain boundary cracks (see FIG. 2). Further, chromium (Cr) may
contribute to precipitation hardening of intermetallic compounds
especially when heat treatment is performed at 700.degree. C. or
lower. However, when the content of chromium (Cr) is smaller than
0.05%, the crack prevention effect may be exhibited during hot
rolling, but the hardening effect may be significantly reduced.
Thus, the purpose of the addition thereof is not achieved. To the
contrary, when the content of chromium (Cr) exceeds 0.5%, Cr is not
fully formed a solid solution in the copper (Cu) matrix in all
temperature regions and thus a micrometer-sized coarse
intermetallic compound may be formed. The coarse intermetallic
compound thus formed may cause non-uniformity of a microstructure
and thus deteriorate punchability and bending formability. Further,
the coarse intermetallic compounds tend to absorb chromium (Cr),
cobalt (Co), and nickel (Ni) and thus grow during precipitation
heat treatment, thereby reducing formation of fine precipitates.
This leads to decrease in the precipitation hardening effect.
[0031] In this regard, it may be identified referring to FIG. 2
which is a graph showing a phase fraction based a temperature in a
composition (Example 1) according to the present disclosure, that a
phase fraction of Cr--Si precipitates starts to increase at a
temperature lower than 1000.degree. C., that is, about 980.degree.
C., and Cr--Si precipitates is formed at about 0.002 mol at a
temperature below 700.degree. C.
[0032] (5) Sum of Contents of Nickel and Cobalt (Ni+Co)
[0033] Nickel (Ni) and cobalt (Co) are main elements that form the
intermetallic compound with silicon (Si). 0.2% proof stress value
tends to increase as the sum thereof increases. However, when the
sum of the contents of nickel (Ni) and cobalt (Co) is smaller than
1.5%, it is difficult to satisfy target 0.2% proof stress. To the
contrary, When the sum of the contents of nickel (Ni) and cobalt
(Co) exceeds 2.6%, a temperature which complete solid solution heat
treatment is performed must be increased to 1030.degree. C. or
higher, which is close to a melting point of copper. Thus, the
elements may be molten during hot rolling. Therefore, the total
amount (Ni+Co) of nickel and cobalt is preferably in a range of 1.5
to 2.6%.
[0034] (6) Ratio (Ni/Co) Between Contents of Nickel and Cobalt
[0035] In the copper alloy according to the present disclosure, a
precipitation temperature range of the intermetallic compound may
be controlled based on the ratio between the contents of nickel and
cobalt (Ni/Co). The ratio between contents of nickel and cobalt
(Ni/Co) is in a range of 0.8 to 1.3.
[0036] When the ratio between the contents of nickel and cobalt
(Ni/Co) is smaller than 0.8, a precipitation rate becomes too fast
and thus it is difficult to control a condition under which a
target property is achieved. When the ratio between the contents of
nickel and cobalt (Ni/Co) exceeds 1.3, precipitation of the
intermetallic compound containing cobalt (Co) as a main component
may not occur, so that it is difficult to secure conductivity of
55% IACS or higher.
[0037] (7) Relationship Between Contents of Nickel (Ni), Cobalt
(Co), Silicon (Si) and Chromium (Cr)
[0038] In the copper alloy sheet material according to the present
disclosure, a relationship between the contents of nickel (Ni),
cobalt (Co), silicon (Si) and chromium (Cr) is as follows:
3.5.ltoreq.(Ni+Co)/(Si-Cr/3).ltoreq.4.5.
[0039] When a value of (Ni+Co)/(Si-Cr/3) is smaller than 3.5, the
content of Si is too high, it is easy to obtain high strength,
whereas conductivity is significantly reduced. Further, silicon
oxide may be formed on a surface during casting, thereby to cause
crack during hot rolling. When the value of (Ni+Co)/(Si-Cr/3)
exceeds 4.5, it is difficult to secure conductivity of 50% IACS or
higher.
[0040] (8) Other Elements
[0041] In one example, at least one of manganese (Mn), phosphorus
(P), magnesium (Mg), tin (Sn), zinc (Zn), and zirconium (Zr) may be
optionally added as optional other elements to the alloy as
needed.
[0042] Manganese (Mn) may be contained in 0.01 to 0.2% content.
Manganese (Mn) may have a solid solution hardening effect on the
copper alloy. Further, when phosphorus (P) is added to the alloy, a
fine Mn--P intermetallic compound may be formed in the grain
boundary, thereby suppressing crack during hot rolling. However,
this effect may not be expected when a content of Mn is smaller
than 0.01%. When the content of Mn exceeds 0.2%, conductivity may
be significantly lowered and coarse manganese oxide may be formed
during casting, thereby to cause crack during casting.
[0043] When P is added to the content, the content of phosphorus
(P) is in a range of 0.01 to 0.2%. When the appropriate amount of
phosphorus (P) is added to the alloy, P may react with oxygen in a
molten metal to form a fine oxide, thereby to achieve an effect of
reducing a size of a cast texture. Further, P may lower an oxygen
content in the copper alloy ingot, thereby to achieve an effect of
suppressing hydrogen induced cracking. However, when the content of
phosphorus (P) as added is smaller than 0.01%, it is difficult to
expect such an effect. To the contrary, When the content of P
exceeds 0.2%, the excessive P may rapidly lower the melting point
of the alloy, thereby causing an eutectic reaction to form
phosphide such as Co--P and Ni--P. This reduces the contents of
cobalt (Co) and nickel (Ni) in the matrix, and suppresses
precipitation hardening effect due to Co--Ni--Si intermetallic
compound. Therefore, the content of phosphorus (P) is in a range of
0.01 to 0.2%.
[0044] When Mg is added to the alloy, a content of magnesium (Mg)
is in a range of 0.01 to 0.2%. Magnesium (Mg) forms an
intermetallic compound with silicon (Si), thereby to further
improve the hardness and conductivity of the alloy. When the
addition amount of Mg is smaller than 0.01%, this effect is
insignificant. When the content of Mg exceeds 0.2%, there is a risk
of lowering the bending formability. Therefore, the content of
magnesium (Mg) is in a range of 0.01 to 0.2%.
[0045] When Sn is added to the alloy, the content of tin (Sn) is in
a range of 0.01 to 0.2%. Tin (Sn) may be added as a solid solution
hardening element. It is difficult to expect such an effect when
the content of Sn is smaller than 0.01%. When the content of Sn
exceeds 0.2%, it is difficult to secure conductivity of 55% IACS or
higher.
[0046] When Zn is added to the alloy, the content of zinc (Zn) is
in a range of 0.01 to 0.5%. Zinc (Zn) may act as a solid solution
hardening element and increases corrosion resistance. When the
content of Zn is smaller than 0.01%, there is little hardening
effect. When the content thereof exceeds 0.5%, conductivity may be
lowered.
[0047] When Zr is added to the alloy, the content of zirconium (Zr)
is in a range of 0.01 to 0.1%. Zirconium (Zr) may not lower the
conductivity and may have a similar effect to that of phosphorus
(P). That is, Zr refines the cast texture and lower the oxygen
content. When the content thereof is smaller than 0.01%, such an
effect may be reduced. When the content of Zr exceeds 0.1%, Zr
reacts with cobalt (Co) and nickel (Ni) to form a coarse
intermetallic compound.
[0048] A sum of these other elements is up to 1.0%. When the sum of
these other elements exceeds 1.0%, the strength or conductivity of
the finally obtained copper alloy sheet material is significantly
lowered, which is not preferable.
[0049] (8) Copper and Inevitable Impurities
[0050] The copper alloy sheet material according to the present
disclosure contains a balance amount of copper (Cu) and inevitable
impurities in addition to the above-described components.
Inevitable impurities refer to lead (Pb), arsenic (Sb), carbon (C),
and chlorine (Cl), which are inevitably contained in a raw material
of the copper alloy sheet material or introduced during heat
treatment and rolling. Since the content of the inevitable
impurities is controlled to 0.05% or smaller, the effect thereof on
the final obtained copper alloy sheet material is negligible.
[0051] Next, the method of producing the copper alloy sheet
material according to the present disclosure is described with
reference to FIG. 1.
[0052] First, the component elements are added and molten as
components of the copper alloy sheet material of the present
disclosure as described above. The molten metal is subjected to a
cast process to form an ingot. In the melting step, raw materials
may be heated at 1200 to 1300.degree. C. so that the raw materials
may be completely molten. When the melting temperature is too low,
fluidity of the molten metal may deteriorate. To the contrary, when
the melting temperature is too high, oxidation of highly oxidizable
elements such as chromium (Cr) and cobalt (Co) occurs, thereby
making it difficult to obtain a copper alloy with a desired
composition. After the casting process, it is preferable to slowly
cool the ingot at a rate of 20.degree. C./s or lower over a
temperature range of 700.degree. C. or higher. This is because,
when rapid cooling is performed immediately after the casting step,
a volume variation may occur due to a difference between
temperatures of a surface and an inner portion of the ingot,
thereby to cause crack in the ingot.
[0053] Subsequently, the cast ingot is hot rolled at 950 to
1040.degree. C. When hot rolling is performed at a temperature
lower than 950.degree. C., there is a possibility that the
intermetallic compound precipitates in the grain boundary and thus
cracks occur. When the hot rolling is performed at temperatures
exceeding 1040.degree. C., a final solidification point may be
molten at the time of casting, thereby to cause red shortness.
[0054] Subsequently, the sheet material obtained via the
hot-rolling is cooled. The cooling may be performed at a rate of 10
to 50.degree. C./s to a temperature below 300.degree. C. When the
cooling rate after the hot rolling is smaller than 10.degree. C./s,
the intermetallic compound precipitates in a large amount and thus
the solid solubility of the elements may be lowered in the solid
solution heat treatment, so that the strength of the finally
obtained copper alloy sheet material is reduced. When the cooling
rate exceeds 50.degree. C./s, intermetallic compounds are
precipitated in a small amount, so that it is difficult to obtain a
cube texture whose a crystal face of a rear face is mainly {200}
during the solid solution heat treatment. Thus, bending formability
may be deteriorated.
[0055] Subsequently, the copper alloy in a form of a cooled strip
is cold rolled at a cold reduction rate of 70% or greater. When the
cold reduction rate is lower than 70%, it is difficult to obtain
desired properties in the solid solution heat treatment, which will
be described later and it is difficult to ensure a target thickness
of the final product.
[0056] Subsequently, the cold rolled sheet material is subjected to
the solid solution heat treatment for 20 to 60 seconds at a
temperature condition of 800 to 1040.degree. C. When the solid
solution heat treatment temperature is below 800.degree. C., it is
easy to secure conductivity during the precipitation heat
treatment, while the strength tends to be low. When the solid
solution heat treatment temperature exceeds 1040.degree. C., the
opposite trend may occur. That is, it is easy to secure strength,
but tends to decrease conductivity. When solution heat treatment
time is smaller than 20 seconds, the bending formability decreases
because the cold rolled texture does not disappear completely. When
the time is larger than 60 seconds, it is difficult to secure
conductivity and strength due to the difficulty in forming
precipitates due to grain coarsening.
[0057] The solid solution heat-treated sheet material is subjected
to a thermal-mechanical double aging (TMDA) process. The TMDA
process refers to a series of processes in which first
precipitation heat treatment, cold rolling, and second
precipitation heat treatment are performed, thereby to effectively
achieve both of conductivity and 0.2% proof stress of the finally
obtained copper alloy sheet material.
[0058] Since the TMDA process requires two precipitation heat
treatment processes, the TMDA process has not been conventionally
introduced in the copper alloy sheet material production process.
This is because, in order to perform precipitation heat treatment
of the copper alloy, it takes several hours to several days to
operate a facility, so that performing the precipitation heat
treatment twice or more is considerably disadvantageous in terms of
cost and productivity. However, in accordance with the present
disclosure, the first precipitation heat treatment is performed
under control of a condition of the first precipitation heat
treatment temperature together with the control of the contents of
the alloy elements, while the first precipitation heat treatment
time is set to a short time duration smaller than 60 seconds, so
that price competitiveness and productivity may be secured. The
complex controls of the content and process conditions have never
been disclosed conventionally.
[0059] In the production method according to the present
disclosure, in the first precipitation heat treatment of the TMDA
process, heat treatment of the product obtained in the previous
step is performed at 550 to 700.degree. C. for 20 to 60 seconds.
The intermetallic compound that precipitates during the first
precipitation heat treatment does not precipitate in divided manner
into Co--Si and Ni--Si but precipitates in Ni--Co--Si form in a
mixed manner. Percentages of components of the compound may vary
depending on a precipitation temperature range and the ratio of
contents of Ni and Co (Ni/Co). This is identified via thermodynamic
calculation of the molar fraction as disclosed in FIG. 3 and FIG. 4
as described below.
[0060] When the temperature and time of the first precipitation
heat treatment are not sufficient, the formation of Ni--Co--Si
precipitates mainly containing cobalt (Co) is insufficient during
the first precipitation heat treatment process, so that it is
difficult to secure the conductivity of the finished sheet
material. To the contrary, when the temperature and time of the
first precipitation heat treatment are too high and too long
respectively, the amounts of the alloy elements in the matrix are
small, and thus the strength increase amount during the cold
rolling is significantly reduced and thus the precipitation of
coarse precipitates may occur during the second precipitation heat
treatment, such that the 0.2% proof stress of the finished sheet
material is unlikely to exceed 720 MPa.
[0061] Subsequently, the first precipitation heat-treated sheet
material is cold-rolled at a cold reduction rate of 10 to 50%. When
the cold rolling is performed at a cold reduction rate smaller than
10%, it is difficult to expect an effective strength increase. When
the cold rolling is carried out at a cold reduction rate above 50%,
the 0.2% proof stress may exhibit a very good strength with 850 MPa
or greater, but the bending formability is significantly reduced.
Further, the second precipitation heat treatment time is too long.
When the second precipitation heat treatment time is too long,
there is a disadvantage that a cost required to operate the
equipment increases and thus productivity decreases.
[0062] Subsequently, the cold rolled sheet material is subjected to
the second precipitation heat treatment at 300 to 550.degree. C.
for 1 to 24 hours. In this connection, a temperature at which the
maximum hardness is achieved may vary depending on the cold rolling
cold reduction rate in the TMDA process. When the cold reduction
rate is close to 50%, the second precipitation heat treatment
should be close to 300.degree. C. in order to achieve the maximum
hardness. In this connection, the corresponding required heat
treatment time is tens of hours. To the contrary, when the cold
reduction rate is close to 10%, the second heat treatment should be
performed at a relatively higher temperature while the second
precipitation heat treatment time should be relatively short, for
example, several hours. When conductivities of two sheet materials
as obtained at different second precipitation treatment
temperatures have similar levels, the 0.2% proof stress of the
sheet material obtained under a lower second precipitation
treatment temperature is relatively high. However, when the second
precipitation heat treatment is performed under the above-described
condition range, it is possible to achieve the balance between the
strength and the conductivity required for a recent copper alloy
sheet material.
[0063] Therefore, the sheet material having the desired physical
properties may be obtained via the strict control of the process
conditions of the first precipitation heat treatment, cold rolling
and second precipitation heat treatment of the TMDA process as
described above.
[0064] In relation to the TMDA process, FIG. 3 is a graph showing a
molar fraction of each of elements of Ni--Co--Si precipitates based
on the first and second precipitation heat treatment temperatures
for the composition (Ni/Co=1.22) of Example 1. In this regard, the
present inventors have identified based on thermodynamics
experiment that a reference temperature around which a molar
fraction changes is a temperature range of 550.degree. C. to
700.degree. C. depending on the Ni/Co ratio. As shown in FIG. 3,
for the composition of Example 1, 630.degree. C. is the reference
temperature. In FIG. 3, when the precipitation temperature is
higher than about 630.degree. C., Ni--Co--Si precipitates mainly
containing Co are formed. When the precipitation temperature is
lower than about 630.degree. C., the ratio between the contents of
Co and Ni is reversed, such that Ni--Co--Si precipitates mainly
containing Ni are formed. Therefore, it may be identified that it
is preferable to perform the TDMA process at about 550.degree. C.
or lower in order to easily form Ni--Co--Si precipitates with the
increased Ni molar fraction. That is, it may be seen that it is
possible to simultaneously secure precipitates having different
elemental composition ratios and thus contribute to the improvement
of strength and conductivity. In accordance with the present
disclosure, in order to achieve the purpose of the present
disclosure via thermodynamic calculation and design, the first
precipitation heat treatment is configured to performed in a
temperature range in which precipitates mainly containing cobalt
(Co) may be obtained from Ni--Co--Si precipitates. Then, the second
precipitation heat treatment is configured to be carried out in a
temperature range in which precipitates mainly containing nickel
(Ni) may be obtained from Ni--Co--Si precipitates.
[0065] In one example, when the ratio (Ni/Co) between the contents
of nickel and cobalt is out of the above range as defined according
to the present disclosure, target properties of the copper alloy
sheet material to be achieved in accordance with the present
disclosure may not be achieved even when the precipitation heat
treatment is performed according to the TMDA process conditions as
suggested in accordance with the present disclosure. For example,
FIG. 4 is a graph showing a molar fraction of each of elements of
Ni--Co--Si precipitates based on first and second precipitation
heat treatment temperatures for the composition of Comparative
Example 8 (Ni/Co weight ratio 0.54). It may be identified based on
FIG. 4 that Ni--Co--Si mainly containing cobalt (Co) is formed
regardless of the precipitation heat treatment temperature.
Therefore, in this case, even when the second precipitation heat
treatment is performed, precipitation of Ni may not occur. Thus,
Ni--Co--Si precipitates which mainly contains Co grow excessively,
resulting in a sharp decrease in strength.
[0066] Further, when required, processes such as cold rolling,
homogenizing heat treatment, softening heat treatment, surface
cleaning (pickling and polishing), tensile annealing, and tension
leveling may be selected and combined as carried out in a wrought
copper factory.
[0067] Further, depending on the end use of the sheet material,
processes such as plating, stamping, and etching may be added.
[0068] In one example, a microstructure of the copper alloy sheet
material as produced according to the production method disclosed
in the present disclosure contains an .alpha. mother phase and
intermetallic compound particles. The intermetallic compound
particles has an average diameter of 3 .mu.m or smaller. When the
average diameter of the intermetallic compound particles exceeds 3
.mu.m, the particle acts as a concentration site of stress during
bending, which may be a cause of cracking.
[0069] The copper alloy sheet material produced according to the
present disclosure has 720 MPa to 820 MPa of the 0.2% proof stress
as measured in a direction parallel to the rolling direction
thereof, and has conductivity of 55% IACS to 60% IACS, and has a
feature that a 900 bending formability in a direction parallel to
the rolling direction and a direction perpendicular to the rolling
is R/t=0. The characteristics of the strength, conductivity, and
bending formability, as described above may not be achieved at the
same time in the prior art and should be simultaneously achieved
such that the copper alloy sheet material is used for parts of
small electronic products used in the field of electrical and
electronics today. The copper alloy sheet material having all of
these characteristics may have an excellent effect, especially for
an electronic component.
[0070] Specifically, the strength of the copper alloy sheet
material produced according to the present disclosure is improved.
For example, when the sheet material is used for a support in an
electronic component module, the number of semiconductor chips that
may be supported thereon may increase. Further, because the sheet
material has excellent conductivity, the sheet material may be used
for large-current transport parts. In addition, the copper alloy
sheet material produced according to the present disclosure may be
applied to electronic components such as switches and connectors
that require excellent bending formability when designing
components. In addition, the copper alloy sheet material produced
according to the present disclosure may be applied to a USB
terminal, a mobile SIM socket, etc., which require the above
characteristics in combination thereof.
[0071] Subsequently, the present disclosure is described in more
detail based on Examples. Examples are intended to help understand
the present disclosure but are not intended to be limiting of the
present disclosure.
EXAMPLES
Examples 1 to 10
[0072] The component elements based on the composition of Example 1
as shown in Table 1 below were molten and cast under an atmosphere
to produce a copper alloy ingot, and then the ingot was heated in a
heating furnace at 1000.degree. C. for 1 hour and then is hot
rolled to form a sheet material. The hot rolled copper alloy sheet
material was subjected to cold rolling at a cold reduction rate of
98%, thereby to produce a 0.2 mm thick sheet material. Thus,
solution heat treatment of the sheet material was performed at
950.degree. C. for 30 seconds. Subsequently, the obtained product
was water-quenched using a water bath at room temperature.
[0073] Thereafter, the product was subjected to the first
precipitation heat treatment as the first step in the TMDA process
at 640.degree. C. for 30 seconds and then was water-cooled using a
water bath at room temperature. Subsequently, the sheet material of
a thickness having 0.15 mm was produced via cold rolling at a cold
reduction rate of 25%. Finally, the second precipitation heat
treatment was performed at 380.degree. C. for 12 hours. The
obtained copper alloy sheet material was cut into two pieces, each
having a width of 60 mm and a length of 300 mm, which in turn were
used as a specimen.
[0074] Specimens according to Examples 2 to 10 were produced in a
similar manner to Example 1 based on the composition of the
component elements in Table 1 and the process conditions in Table
2.
Comparative Examples 1 to 18
[0075] Specimens of Comparative Examples 1 to 18 were produced in a
similar manner to Example 1 based on the composition of the
component elements in Table 1 and the process conditions in Table
2.
TABLE-US-00001 TABLE 1 Trace of (Ni + Co)/ Examples Ni Co Si Cr
element Ni + Co Ni/Co (Si - Cr/3) Example 1 1.1 0.9 0.54 0.13 -- 2
1.22 4.03 Example 2 1.1 0.9 0.54 0.13 -- 2 1.22 4.03 Example 3 1.1
0.9 0.54 0.13 -- 2 1.22 4.03 Example 4 1.1 0.9 0.54 0.13 -- 2 1.22
4.03 Example 5 1.1 0.9 0.54 0.13 0.1Mn 2 1.22 4.03 Example 6 1.1
0.9 0.54 0.13 0.05P 2 1.22 4.03 Example 7 1.1 0.9 0.54 0.13 .sup.
0.05Mg 2 1.22 4.03 Example 8 1.1 0.9 0.54 0.13 0.1Sn 2 1.22 4.03
Example 9 1.1 0.9 0.54 0.13 0.2Zn 2 1.22 4.03 Example 10 1.1 0.9
0.54 0.13 .sup. 0.05Zr 2 1.22 4.03 Comparative 1.1 0.9 0.54 0.13 --
2 1.22 4.03 Example 1 Comparative 1.1 0.9 0.54 0.13 -- 2 1.22 4.03
Example 2 Comparative 1.1 0.9 0.54 0.13 -- 2 1.22 4.03 Example 3
Comparative 1.1 0.9 0.54 0.13 -- 2 1.22 4.03 Example 4 Comparative
1.1 0.9 0.45 0.13 -- 2 1.22 4.92 Example 5 Comparative 1.1 0.9 0.54
0.3 -- 2 1.22 4.55 Example 6 Comparative 1.1 0.9 0.7 0.13 -- 2 1.22
3.04 Example 7 Comparative 0.7 1.3 0.54 0.13 -- 2 0.54 4.03 Example
8 Comparative 0.7 0.6 0.38 0.13 -- 1.3 1 .17 3.86 Example 9
Comparative 1.4 0.7 0.6 0.13 -- 2.1 2.00 3.77 Example 10
Comparative 1.1 0.9 0.54 0.13 0.6Mn 2 1.2.2 4.03 Example 11
Comparative 1.1 0.9 0.54 0.13 0.5P 2 1.22 4.03 Example 12
Comparative 1.1 0.9 0.54 0.13 0.6Mg 2 1.22 4.03 Example 13
Comparative 1.1 0.9 0.54 0.13 0.6Sn 2 1.22 4.03 Example 14
Comparative 1.1 0.9 0.54 0.13 0.6Zn 2 1.22 4.03 Example 15
Comparative 1.1 0.9 0.54 0.13 0.5Zr.sup. 2 1.22 4.03 Example 16
Comparative 1.1 0.9 0.7 0.6 -- 2 1.22 4 Example 17 Comparative 1.1
0.9 0.5 -- -- 2 1.22 44 Example 18
TABLE-US-00002 TABLE 2 Thermal-mechanical double aging (TMDA) Hot
Cold rolling Solution First Cold Second rolling cold reduction heat
precipitation reduction precipitation temperature rate treatment
temperature rate temperature Examples (.degree. C.* 1 h) (%)
(.degree. C., s) (.degree. C.*1 min) (%) (.degree. C., h) Example 1
1000 98 950, 30 640 25 380, 12 Example 2 1000 98 950, 30 640 25
380, 15 Example 3 1000 98 950, 30 640 25 380, 18 Example 4 1000 98
950, 30 640 25 380, 24 Example 5 1000 98 950, 30 640 25 380, 15
Example 6 1000 98 950, 30 640 25 380, 15 Example 7 1000 98 950, 30
640 25 380, 12 Example 8 1000 98 950, 30 640 25 380, 15 Example 9
1000 98 950, 30 640 25 380, 15 Example 10 1000 98 950, 30 640 25
380, 18 Comparative 850 Not performed due to crack occurring in hot
rolling Example 1 Comparative 1000 98 750, 50 640 25 380, 12
Example 2 Comparative 1000 98 950, 30 800 25 380, 12 Example 3
Comparative 1000 98 950, 30 640 Not performed 380, 12 Example 4
Comparative 1000 98 950, 30 640 25 380, 12 Example 5 Comparative
1000 98 950, 30 640 25 380, 12 Example 6 Comparative 1000 98 950,
30 640 25 380, 12 Example 7 Comparative 1000 98 950, 30 640 25 380,
12 Example 8 Comparative 1000 98 950, 30 640 25 380, 12 Example 9
Comparative 1000 98 950, 30 640 25 380, 12 Example 10 Comparative
1000 98 950, 30 640 25 380, 12 Example 11 Comparative 1000 98 950,
30 640 25 380, 12 Example 12 Comparative 1000 98 950, 30 640 25
380, 12 Example 13 Comparative 1000 98 950, 30 640 25 380, 12
Example 14 Comparative 1000 98 950, 30 640 25 380, 12 Example 15
Comparative 1000 98 950, 30 640 25 380, 12 Example 16 Comparative
1000 98 950, 30 640 25 380, 12 Example 17 Comparative 1000 98 950,
30 640 25 380, 12 Example 18
EXPERIMENTAL EXAMPLES
[0076] The characteristics of the specimens of the copper alloy
sheet materials produced according to Examples and Comparative
Examples were evaluated.
[0077] To evaluate the strength, the specimen was reworked
according to a tensile test (ISO 6892) and then a test was
performed.
[0078] Further, in order to investigate the conductivity, the
conductivity of the specimen was measured using a conductivity
meter (Sigmatest 2.069) from Forester corporation.
[0079] Further, to measure a size of intermetallic compound
particles, a microstructure was observed using a scanning electron
microscope from JEOL corporation. When a particle having an average
diameter larger than 3 .mu.m was found, O was marked, while when
not, X was marked.
[0080] In a bending formability test (JIS H 3130), a W bending test
was performed in which a bending axis is the same direction (bad
way) as a rolling direction. When a ratio of a radius (R) of a bent
portion to a thickness (t) thereof is 0 (that is, 90.degree.
R/t=0), crack does not occur. In this case, O was marked. When a
crack occurs, X was marked.
[0081] The measurement results of the characteristic evaluation are
shown in Table 3 below.
TABLE-US-00003 TABLE 3 Properties of finished sheet material
Microstructure 0.2% Presence or proof Bending absence of
Conductivity stress formability precipitate Examples (% IACS) (MPa)
(90.degree. R/t = 0) larger than 3 .mu.m Example 1 55.1 812
.largecircle. X Example 2 55.9 793 .largecircle. X Example 3 57.2
772 .largecircle. X Example 4 58.3 735 .largecircle. X Example 5
55.3 822 .largecircle. X Example 6 56.5 809 .largecircle. X Example
7 56 803 .largecircle. X Example 8 55 815 .largecircle. X Example 9
55.2 811 .largecircle. X Example 10 57.6 783 .largecircle. X
Comparative Not performed due to crack occurring in hot rolling
Example 1 Comparative 56.2 704 .largecircle. X Example 2
Comparative 52 793 .largecircle. X Example 3 Comparative 52 786
.largecircle. X Example 4 Comparative 49 820 .largecircle. X
Example 5 Comparative 56 719 X .largecircle. Example 6 Comparative
46 845 .largecircle. X Example 7 Comparative 59.5 702 .largecircle.
X Example 8 Comparative 60.1 675 .largecircle. X Example 9
Comparative 47.6 848 X X Example 10 Comparative 47.2 855
.largecircle. X Example 11 Comparative 59 704 X .largecircle.
Example 12 Comparative 49 852 X X Example 13 Comparative 45 860 X X
Example 14 Comparative 52 805 .largecircle. X Example 15
Comparative 58 709 X .largecircle. Example 16 Comparative 51 762 X
.largecircle. Example 17 Comparative 59.3 651 .largecircle. X
Example 18
[0082] As shown in Table 3, in the copper alloy sheet materials
obtained according to Examples 1 to 9, a size of the intermetallic
compound does not exceed 3 .mu.m, conductivity is larger than 55%
IACS, and 0.2% proof stress is larger than 720 MPa. Further, the
90.degree. bending formability has R/t=0, thus, the sheet materials
may be used for an electronic component having a bent portion such
as a connector.
[0083] However, in Comparative Example 1, the hot rolling
temperature was remarkably low, and thus side cracks were induced
along the grain boundary. Thus, the process after the hot rolling
could not be performed.
[0084] In Comparative Example 2, the solid solution heat treatment
temperature is low and is 750.degree. C., a large amount of fine
intermetallic compound particles may be formed during precipitation
heat treatment due to a small amount of supersaturated Co and Ni
atoms. Thus, 0.2% proof stress 720 MPa may not be secured.
[0085] In Comparative Example 3, the first precipitation heat
treatment temperature in the thermal-mechanical double aging
process was a relatively low temperature of 500.degree. C. As a
result, the conductivity was found to be 55% IACS or lower. This is
because the precipitation heat treatment was not performed in the
temperature range where precipitation of Co may occur.
[0086] In Comparative Example 4, the cold rolling between the first
and second precipitation heat treatments did not occur. After the
second precipitation heat treatment, the finishing cold rolling was
performed at a 25% cold reduction rate. As a result, both of the
conductivity 55% IASC, and 0.2% proof stress 720 MPa were not
obtained at the same time. This is because after the second
precipitation heat treatment, the number of solid solution formed
atoms on the matrix was significantly reduced, such that work
hardening via the cold rolling was not effective.
[0087] In Comparative Example 5 and Comparative Example 6, the
(Ni+Co)/(Si-Cr/3) value exceeded the range suggested in accordance
with the present disclosure. Therefore, an effective intermetallic
compound formation did not occur, and, thus, Ni and Co are present
as the remainders in the matrix, thereby not to secure the target
conductivity.
[0088] In Comparative Example 7, the (Ni+Co)/(Si-Cr/3) value was
3.04 which was smaller than the range suggested in accordance with
the present disclosure. As a result, Si that failed to combine with
Ni and Co to form Ni--Co--Si remains as the remainder, thereby
lowering conductivity.
[0089] In Comparative Example 8, the Ni/Co ratio was smaller than
the range suggested in the present disclosure. Therefore, a
precipitation rate of the Ni--Co--Si intermetallic compound
containing a large amount of Co becomes too high. Thus, the
conductivity may be secured. However, it is difficult to refine the
precipitates, such that the strength is rapidly reduced.
[0090] In Comparative Example 9, the sum of Ni and Co contents was
smaller than the range suggested in the present disclosure.
Therefore, coarse intermetallic compounds were not formed and thus
conductivity is relatively high. However, a large amount of fine
intermetallic compounds was not formed, thereby not to satisfy 0.2%
proof stress 720 MPa.
[0091] In Comparative Example 10, the Ni/Co ratio exceeded the
range suggested in the present disclosure. When the content of Ni
increases, the precipitation temperature at which the Ni--Co--Si
compound having a high Co content is formed increases, thereby
making Co precipitation via the first precipitation heat treatment
difficult. Therefore, the conductivity was lowered.
[0092] In Comparative Example 11 to Comparative Example 16, the
content of each of the component elements exceeds a range defined
according to the present disclosure, resulting in poor
conductivity, or resulting in reduced bending formability due to
formation of coarse intermetallic compounds.
[0093] In Comparative Example 17, the alloy has the Cr content
exceeding the range defined according to the present disclosure.
Thus, the conductivity decreases, and the bending formability is
lowered.
[0094] In Comparative Example 18, Cr as an essential element
suggested in the present disclosure was added to the alloy. Thus,
it is easy to secure the conductivity due to increase in a purity
of the matrix. However, 0.2% proof stress 720 MPa is not
realized.
* * * * *